1. Field of the Invention
The present invention is generally related to a composite film and method thereof, and more particularly to a semicrystalline polymer/graphene oxide composite film and method thereof.
2. Description of the Prior Art
Accompanying with the advance of technologies, new mobile or portable information electronic products keep continuously emerging and a flat panel display thereon has to be applicable to the flexible display technology and flexible electronic devices in addition to being light, thin, compact, etc.
A barrier film is a barrier layer to block gas and moisture from flowing so as to keep gas and moisture on one side of the film. Therefore, such a barrier film can be applied in food wrapping, packaging, solar cells, flexible displays, etc. and plays an important role in electronic and packaging industries. Since organic and metallic substances usually used in electronic industries are sensitive to oxygen and moisture, passage of moisture and oxygen may cause metal in electronic components to oxidize so as to affect performance of a display and shorten lifetime of a display. Therefore, an electronic product should be properly packaged for suitable protection.
A flexible display becomes the current trend for a new era of display research where the substrate for a flexible display is a flexible plastic substrate instead of glass. However, there are many manufacturing problems to be conquered in order to provide a usable reliable flexible plastic substrate. Among these, a flexible plastic substrate having high transparency and high size stability is urgently needed. The size stability and limitation of operational temperature of a flexible plastic substrate is a big limiting factor. On the other hand, gas barrier processing for a flexible plastic substrate is one other key factor to determine the lifetime of a flexible display and to maintain display quality.
Besides, it is reported that polyvinyl alcohol being a water soluble polymer to be high hydrophilic, biocompatible, nontoxic, and capable of film forming (H. M. Kim, J. K. Lee, H. S. Lee, Transparent and high gas barrier films based on poly(vinyl alcohol)/graphene oxide composites, Thin Solid Films, In Press, Corrected Proof.). A polyvinyl alcohol film has the characteristics of high transparency (transmittance >90%) and being a good gas barrier. In addition, it is a dense film with high crystallinity and has good adhesiveness, oil and solvent resistance. Regarding its mechanical properties, a polyvinyl alcohol film has good toughness and large tensile strength (44.1˜63.7) to have good tear resistance among various plastic films so as to be extensively used in food packaging. However, the polyvinyl alcohol film fulfills the requirements as a gas barrier for food packaging but requires further improvement for electronic industries, such as functioning as a substrate of a flexible display.
Furthermore, oxygen transport and free volume in cold-crystallized and melt-crystallized poly(ethylene naphthalate) (PEN) is reported by Y. S. Hu, R. Y. F. Liu, L. Q. Zhang, M. Rogunova, etc. (Macromolecules 2002, 35, 7326-7337) where crystallization enhances gas barrier property of PEN even for small gas molecules. A Study of the Gas Barrier Properties of Highly Oriented Polyethylene is reported by P. S. HOLDEN, G. A. J. ORCHARD, I. M. WARD, etc. (Journal of Polymer Science: Polymer Physics Edition, Vol. 23,709-731 (1985)) where crystallization enhances gas barrier property of polyethylene film even for small gas molecules.
A graphene-made film has high gas barrier property as well but it lacks transparency and flexibility when its film thickness becomes thicker. Therefore, a graphene film cannot be standalone as a gas barrier and may be suitable to combine with other polymers such as polyvinyl alcohol to be used as a composite material to maintain gas barrier property together with transparency.
On the other hand, a gas barrier film with high transparency formed by blendng polyvinyl alcohol water soluble polymer with clay is reported but the gas barrier film becomes brittle to be unsuitable in flexible applications because there are a lot of clay needed to have the gas blockage effect. Besides, a composite film formed by mixing polymer with layered graphene oxide is not reported.
Therefore, it is urgently needed to have a good gas barrier film with high transparency suitable to be coated on a substrate for a flexible display.